This invention relates to articulated crane-type machines, such as hydraulic excavators, and is more particularly directed to machines of the type having a front boom attachment. The invention is also directed towards derrick-type machines.
A derrick or similar lifting machine is often required on a building or construction site on which an excavator is also used. Normally, two separate machines, a derrick crane and an excavator, are transported to the site.
However, because of the high cost of these machines and the time and difficulty in transporting them, it is desired to find some suitable way to adapt the boom of an excavator for use as a derrick, so that one such machine can double on the other. That is, some means for attaching a cable and winch, with a block or sheave suspended from the boom. Preferrably, the radial position of the block or sheave along the boom should be adjustable to facilitate level transfer of an item being hoisted or lifted by the derrick. Using conventional techniques, it would be required to raise or lower the boom and at the same time to pay out or take up cable to maintain the carried object in a level plane. This is a slow and complex operation.